The present invention relates to a transmission apparatus, a reception apparatus, and a transmission and reception method for same, and in particular relates to a transmission apparatus comprising a retransmission function to transmit new data or retransmit transmitted data based on normal/abnormal reception result data sent from a reception apparatus, a reception apparatus comprising a data transmission interval modification request function, and a transmission and reception method for these.
In packet transmission, error detection codes are used in order to enhance the reliability of communication, and an automated retransmission request (ARQ, Automatic Repeat Request) method is adopted in which the transmitting side is made to retransmit data when an error is detected on the receiving side (see for example JP 2002-9741A).
FIG. 20 is an explanatory diagram of the processing procedure for a Stop-and-Wait ARQ method, which is a basic ARQ method. For simplicity, processing at the transmitting station and receiving station are classified into three processing types, which are transmission processing, reception processing, and decoding processing. The functions of these are as follows.
Transmission processing: Data modulation, error correction encoding, and similar
Reception processing: synchronous acquisition of data and similar
Decoding processing: Data decoding, error correction decoding, error detection, and similar
First, the transmitting station transmits to the receiving station one frame of data (called data 1), which is a transmission data unit, and the receiving station performs reception processing and decoding processing. Next, based on the error detection result, the receiving station transmits to the transmitting station through the control channel an ACK or a NACK signal, which is the reception result for data 1, and the transmitting station performs reception processing and decoding processing for the control channel. At the transmitting station, when a NACK signal is received, data 1 is retransmitted to the receiving station, and when an ACK signal is received, data 2, which is new data, is transmitted.
Here, the time required from the first transmission of data 1 to the retransmission of data 1, or to the first transmission of data 2, is called the Round Trip Time (RTT), that is, the retransmission interval. In the Stop-and-Wait ARQ method, new data or retransmitted data is transmitted in RTT intervals, so that transmission efficiency is low.
FIG. 21 explains the processing procedure for N channel Stop-and-Wait ARQ, which is an improved version of Stop-and-Wait ARQ. By preparing several frames in the retransmission buffer of the transmitting station, the next frame of data can be transmitted without waiting for a report of the data reception result (ACK or NACK signal) for a certain frame, so that transmission efficiency is comparatively high. At the receiving station, in order to process data which is transmitted continuously in this way, pipeline processing is used for the three types of processing which are reception, decoding, and transmission, and each processing operation must end within one frame.
The technology disclosed in JP 2002-9741A is an ARQ method having as an objective improvement of transmission characteristics using ACK/NACK signals. In this ARQ method, the receiving side determines reliability information in demodulated packets, performs error detection, and uses the error detection results and packet reliability information to create ACK/NACK signals, indicated in three or more levels, which are returned to the transmitting side. The transmitting side performs judgment of ACK or NACK signals, and based on the judgment results transmits a new packet or performs retransmission control.
Technology to realize ultra-high speed data transmission and to raise frequency utilization efficiency to the limit, such as for example Orthogonal Frequency Division Multiplexing (OFDM), Multiple-Input Multiple-Output (MIMO) multiplexed transmission, turbo-encoding, Low-Density Parity Check (LDPC) encoding, and similar are being applied to next-generation and future-generation mobile communication systems. Hence because MIMO signal separation, multistage decoding, repeat decoding, and other advanced and complex signal processing is performed at the receiving station, the amount of computation required for decoding processing is enormous.
In order to apply the above-described retransmission control algorithm to such a mobile communication system, the following two requirements must be met.
The first requirement is that, regardless of the enormous amount of computation for decoding processing, the receiving station must complete processing of data sent continuously from the transmitting station within one frame. To this end, a method of performing decoding processing in parallel is conceivable. Also, for processing which cannot easily be performed using parallel processing, such as for example processing in a plurality of stages and repeated decoding, methods such as increasing the number of pipeline stages and increasing the RTT are conceivable. FIG. 22 explains the processing procedure when decoding processing is performed using two-stage pipeline processing. In FIG. 22, by performing two stages of decoding processing using two pipelines for processing, each processing at the receiving station is completed within one frame. As a result, data sent continuously from the transmitting station can be processed.
The second requirement is that the time from data transmission to the reception of an ACK signal (the transmission delay) be short. This is of course a requirement when transmitting media for which real time properties are emphasized, as in the case of video; but even when transmitting media without such real time properties, because of the fast transmission rate, it is desirable that the transmission delay be short in order to limit the retransmission buffer capacity of the transmitting station to a realistic size.
Here, the relation between the number of stages of decoding processing and the transmission delay is considered. If the number of stages is increased the RTT is lengthened, and so when there is a NACK judgment for transmitted data the transmission delay increases. Hence it seems at first that as the number of stages of decoding processing increases, the transmission delay increases. However, in actuality, as the number of stages of decoding processing increases the characteristic is significantly improved, so that the probability of a NACK judgment declines. For example, in the case of turbo code, the greater the increase in the number of decoding repetitions, the more the error rate declines. Hence the RTT is lengthened, but the number of retransmissions decreases, and so it is thought that the overall transmission delay is shortened.
FIG. 23 shows the configuration of a receiving station of the prior art which satisfies the above first and second requirements, and is an example in which decoding processing is performed in three stages. The reception processing circuit 1 performs synchronous acquisition of data and other reception processing. The decoding processing circuit 2 performs error correction decoding and other decoding processing through decoding processing in three stages, which are stages 1 to 3. This decoding processing circuit 2 achieves the required reception characteristic, and employs parallel processing and pipelines to complete processing within one frame. The error detection circuit 3 performs error detection of output signals from the decoding processing circuit 2, and outputs a NACK signal when an error is detected, but outputs an ACK signal when no errors are detected. The transmission processing circuit 4 maps the ACK signal or NACK signal to the control channel, performs data modulation and similar, and transmits data to the transmitting station. By means of this configuration in FIG. 23, continuously transmitted data can be processed, and the transmission delay can be kept short.
However, there have been increases in the circuit scale of receiving stations, such as for example portable mobile terminals, according to the number of pipelines, degree of parallel processing, and number of decoding stages, resulting in the problems of increased power consumption and higher costs.